The present invention relates to thermal analysis apparatus for measuring changes of physical or chemical characteristics of a sample according to the temperature.
More particularly, the present invention relates to a differential scanning calorimeter for performing analysis by measuring endothermic/exothermic heat accompanying transitions, etc., of a sample as a function of temperature.
With respect to the above differential scanning calorimeters, two kinds such as the heat flux-type and the power compensation-type calorimeters differentiated by the measurement method are well known. The power compensation-type calorimeter is also referred to herein as an input compensation-type calorimeter.
A basic structure for a power compensation-type differential scanning calorimeter is shown in FIG. 3.
Numerals 28 and 29 are holders for mounting a sample and a reference material, and temperature sensors 30, 31 composed of a resistor for temperature detection, etc and heaters 32, 33 for heat flow feedback are provided for each holder.
The thermal signal of each temperature sensor is measured with a temperature measuring instrument 34, the average temperature of the sample side and the reference material side is output to an average temperature controller 35, and the differential temperature is output to a differential thermal controller 36.
In the DSC of this type, control and measurement are performed by two feedback loop systems.
The first feedback loop is for the average temperature, which compares the average temperature between the sample side and the reference material side to the program temperature outputted by the program temperature generator, outputs the power to the heater for heat flow feedback to make both correspond to each other, and then makes changes to both holders according to the temperature program.
The second feedback loop is for differential temperature, and outputs the appropriate power to the sample side heater 32 and the reference material side heater 33 to set the differential temperature outputted by the temperature sensor back to zero.
Specifically, it adjusts the distribution of the power to heat each heater according to the temperature differential while maintaining a constant total amount of power supplied to the sample side heater 32 and the reference material side heater 33, and exerts control to set the temperature differential back to zero.
As a result, when the endothermic phenomenon occurs at the sample side, the power to be supplied to the sample side heater 32 is increased, and the power to be supplied to the reference material side heater 33 is decreased by the same amount.
This power difference is outputted as a sample endothermic/exothermic signal (DSC signal).
For this type of invention of the related art as disclosed in Japanese Patent publication Hei.11-160261, a structure, which comprises a detector constituted by a temperature sensor and a heater for heat flow feedback, where the detector provided inside a heat sink, and performs DSC output using a control loop similar to the above while controlling the heat sink temperature, is already known.
However, with the input compensation-type differential scanning calorimeters of the related art, the distribution of power to be supplied to the sample side and the reference material side is adjusted according to the temperature difference to compensate for the temperature difference between the sample side and reference material side caused by the differential thermal feedback loop. As the amount of power supplied fluctuates even with a non-endothermic reference material, there is therefore a problem that the reference material side temperature also fluctuates.
Moreover, in this type of the input compensation-type differential scanning calorimeter of the related art, power is supplied to both the sample side and the reference material side by the double feedback loops. This causes mutual interference, so that the output of one of the feedback loops influences the other feedback loop, making precise temperature control difficult.
It is the object of the present invention to provide thermal analysis apparatus which resolves the above problems.
To resolve the above problems, a first differential scanning calorimeter relating to the present invention comprises a sample holder for mounting a sample container containing a sample, a sample temperature sensor for measuring the sample temperature, a sample side heater to heat the sample, a reference material holder for mounting the reference material container containing the reference material, a reference material temperature sensor for measuring the reference material temperature, a reference material side heater to heat the reference material, a temperature measuring instrument for measuring the reference material side temperature and the differential temperature between the sample side and the reference material side, a program temperature generator; a reference material side temperature controller for outputting the power to the sample side heater and the reference material side heater based on the result obtained by comparing the reference material side temperature outputted by the reference material temperature measuring instrument to the desired value of the temperature outputted by the program temperature generator, and a differential thermal compensator for inputting the differential temperature outputted by the temperature measuring instrument and outputting the power to the sample side heater to set the value back to zero.
A second differential scanning calorimeter relating to the present invention comprises a sample holder for mounting a sample container containing a sample, a sample temperature sensor for measuring the sample temperature, a sample side heater for heating the sample, a reference material holder for mounting the reference material container containing the reference material, a reference material temperature sensor for measuring the reference material temperature, a reference material side heater to heat the reference material, a temperature measuring instrument for measuring the differential temperature between the sample side and the reference material side, a differential thermal compensator for taking as input the differential temperature outputted by the temperature measuring instrument and outputting the power to the sample side heater to set the value back to zero, a bias power output instrument for outputting the fixed bias power to the sample side heater and the reference material side heater, a heat reservoir surrounding the sample holder and the reference material holder, a heat reservoir temperature measuring instrument for measuring the heat reservoir temperature, a program temperature generator, and a heat reservoir temperature controller for controlling the heat reservoir to make the heat reservoir temperature correspond to the desired value of temperature outputted by the program temperature generator.
With the first configuration, the reference material temperature controller outputs the power to the reference material side heater so that the reference material temperature and the program temperature correspond to each other.
The same amount of power is outputted to the sample side heater and both holders are adjusted according to the temperature program.
When a temperature difference occurs between the sample and the reference material, the differential thermal compensator outputs power to the sample side to set the value back to zero, and detects the power outputted by the differential thermal compensator as the sample endothermic/exothermic signal (DSC signal).
The second configuration brings the effect that the heat reservoir controller controls the heat reservoir to make the heat reservoir temperature and the program temperature correspond to each other.
When a temperature difference occurs between the sample and the reference material, the differential thermal compensator outputs power to the sample side to set the value back to zero, and detects the power outputted by the differential thermal compensator as the sample endothermic/exothermic signal (DSC signal).
As a result, the power to be supplied to the reference material side does not fluctuate due to the endothermic/exothermic phenomena of the sample, so that the reference material side temperature does not fluctuate.
Additionally, the places to be supplied with power can be separated with the two feedback loops, so that the mutual interference between the two feedback loops is prevented and precise temperature control is possible.